Tap reconditioning machine



Jan. 22, 1946. s. B. HELLSTROM 2,393,372

" TAP RECONDITIONING MACHINE Fi led May 20, 1942 4 Sheets-Sheetl INVENTOR 576,27 BHeZZJZ/ww I W I fla A TTORNE is.

s. B. H ELLSTROM TAP RECONDITIONING MACHINE Filed May 20, 1942 4 Sheets-Sheet 2 I mm .W Z Q /m WM 1, H 2 m y. 5

1946- s. B. HELLSTROM TAP RECONDITIONING MACHINE Filed May 20, 1942 4 Sheets-Sheet 3 A TTORNE X Jan. 22, 1946'. s. B. HELLSTROM 3,

" TAP RECONDITIONING MACHINE Filed may 20, 1942 .4 Sheets-Sheet- 4 INVENTOR i zz de q TToRNEya- Patented Jan. 22, 1946 v UNITED; srAT-E TAPRECONDITIONINGEMACHlNE If I Sven B. Hellstrom, Grosse l oi nte Farms, Mich.,, assignor to Detroit Tap & ToolCompany, Detroit, Mich.,.a corporation of Delaware Application May 20, 1942, Serial Nb- 443,818

I v 5 Claims. This invention relates to tap reconditioning machines. j

It is a primary object of the present invention to provide a simple, compact, and yet' at the same time precise and accurate machinecapable of performing all of the necessary operations re-' quired to recondition taps after the same have become worn as a result of use.

Still further, it is an object ofthe present invention to provide a tap reconditioning machine which is capable of performing thedesired grinding and finishing operations necessary. to recon-v dition taps upon taps whichmay vary'widely in size, number of flutes, angle of taper and degree of chamfer. Still further, the invention contemplates the provision of apparatus which may easily and conveniently be adjustedto accommodate taps having various numbers of flutes and taps which are designed for either right or leithand threads. Still further, theinvention contemplates the provision of apparatus which is sufficiently simple in construction so that the same may be operated by relatively unskilled labor. a Many other andfurther objects, advantages, and features of the present invention will become apparent from the following description, when,

considered in conjunction withthe accompanying drawings, wherein: V

Figure 1 is a top plan view with partsin seotion showing one form of apparatusembodying the improvements of the present invention. t

Figure 2 is a front elevational view of ,the apparatus shown in Figure 1 with parts b rok en away and parts in section toillustrate more fully and clearly the construction andarrangement of parts. Figure 3 is an end elevational view of the apparatus shown in Figures 1 and 2 takenfrom the righthand end of the apparatusas shown in these figures. 7

Figure 4 is a fragmentary elevational view showing the main grindin wheel and the apparatus for truing the same. .7

Figure 5 is an end elevational view takenalong line 5-5 of Figure 2 with parts in section showing the head assembly for holding a tap while the chamfer is ground thereon.

Figure 6 is an end elevational view taken along the line 6.-5 of Figure 1 showing in further detail the headassembly for holding a tap while the chamfer is ground thereon.

With more particular reference to the drawings, it must be borne in mind that the drawings disclose but one single embodiment of the invention described and claimed herein and, while the construction shownis quite specific, .many modificationstheredf and departures therefrom may be made without departing from the generic spirit or scope of the'invention as defined in the appended claims.

In the specific embodiment of the invention illustrated in the drawings, theapparatus shown comprises a base. [0 which is preferably formed from a single, integralhollow casting and which serves to provide a rigid support for the tap reconditioning apparatus hereinafter described in detail. .I i I 7 As will hereinafter be more clearly brought out; certain portions of the apparatus are Preferably mounted interiorly-"of the base Hi. This base member ID may obviously be mountedupon or include a pedestalinot shown) if it is desired to support ;the. apparatus directly on the floor of the shop. -On the upper surface of the base in, a motor support It is mounted adjacentone end qf'the base member. An electricmotor i2 is rigidly anchored to the motor supportby means of screws l3, as shown in Figure 2, and, as seen in, Figure 5, the motor may beconveniently supplied with electricicurrent from a suitable flexible conduit, L4; f j

j The motor. support H is slidably'mounted on the base in by. means of ways 15 which serve to permit transverse sliding movement of the motor support and-the motor carried thereby with respect tothe, base member. This sliding movevm ent, itwill be noted, is'in afdirec'tion perpen dicular tov the'axis of rotation of thefmotor. Consequently, as this sliding movement takes place, the motor support and motor willbe bodily shifted in adirection perpendicular to the axis cfthemotor. j

fIhis sliding movementv of the motor is accurately and precisely controlled by means .of a feed screw l6 'journalled, for'rotation in asuitable, upwardly projecting boss l'l formed on" the base I0. This'feed screw H5 is rotatably received by a suitable lead nut anchored'to thefmotor support; "The feed screw includes an'integrally connected, conveniently accessible handle la and it will be" clear from the construction which is describedthat rotation of the handle 18 will serve to cause bodily shifting of the motor support and motor with respect'to the base 40.

In order that the motor support and motor may be,-1ocked in predetermined, adjusted position when desired, a thumb screw I9, seen in Figure 2, I

is provided which serves to positively anchor the motor support in predetermined, adjusted position with respect to the base when it is desired to retain the motor support fixed in predetermined position. The motor 12 has a shaft projecting from each axial end thereof to permit the mounting of two simultaneously operated abrasive wheels, the construction and function of which is hereinafter described in detail.

At the lefthand side of the apparatus, as seen in Figure 2, a generally cylindrical abrasive wheel is mounted on the shaft of the motor. This abrasive wheel is partially surrounded by a housing 2| which is directly connected to the hous ing of the motor I2 in order that as movement of .the motor takes place, the housing will be bodily moved also. Integrally' formed: on the housing 2| is a pair of generally cylindrical bosses, 22 and 23, the forward boss 22 being clearly seen in Figure 2, while both bosses are clearly shown in Figures 1 and 5. The purpose and function of these bosses 22 and 23 are hereinafter described in detail.

As is clearly seen in Figures 1 and 2, the outer axial end of the housing 22 is closed by means of a removable cover plate 24 secured to thehousing by means of screws 25 in order to provide means for gaining access to the housing when it is desired to re-mount'or replace the grinding wheel 20 on the shaft of the motor. The manner in which the housing and cover plate are recessed or cut away to give access to the periphery of the abrasive wheel 20 is clearly seen in Figure 4.

Referring specifically now to Figure 4, it will be seen that a simple, convenient and accurate deviceis provided for truing the surface of the abrasive wheel 20. This device comprises an arm 26 which has permanently and rigidly connected thereto a pivot pin 21 adapted to be received within a hollow bore 28 in the boss 22. The axis of this bore 28, it will be noted, is substantially tangential to the periphery of the grinding wheel. At its outer end,'the arm 26 carries an adjustable screw 29 provided with a diamond point adapted to engage the periphery of the grinding wheel and it will be seen that as the arm 26 is swung about the pivot pin 21, the diamond point on the screw 29cwill be moved transversely across the surface of the abrasive wheel in order to provide the wheel with a substantially true cylindrical surface and it will be seen that as the wheel becomes .worn, the set screw 29 may be adjusted to advance the pointthereof generally radially toward the center-of the abrasive wheel. When not actually in use, the arm 26 may be mounted in inoperative position out oi the way by removing the pin from the bore 28 and inserting the pin. in a similar bore 30 formed in the boss 23.-

As will hereinafter become more clear, this abrasive wheel 20 is designed and intended for grinding the chamfer on the point of a tap, that is; grinding the conical surface'of the land between adjacent fiutes in a tap and it will be appreciated that this surface, while generally conical in form, must be eccentric to the axis of the tap in order to provide the necessary relief back of the cutting edge of the tap point; The portion of the apparatus now to bedescribed is [that which serves to hold the tap to be ground in predetermined position with respect to. the grinding wheel and which. serves to permit movement, of the tap in such a manner that this chami'er may be accurately and precisely ground to the finally desired form.

Referring now to Figure '2, it. will be seen that the base I3 is provided at the forward, lefthand corner thereof with an upwardly extending, generally circular boss 31 which serves to provide means for mounting an outwardly extending bracket 32 which in turn serves to mount the apparatus for holding the tap hereinafter described in detail. As is clearly seen in the drawings, the bracket 32 maybe pivotally adjusted with respect to the base HI and may be anchored in predetermined adjusted position with respect to the base and with respect to the pivot bolt 33.

As is clearly seen in Figure 1, an extending portion of the surface of the boss 3| is provided with graduations generally designated as 34 and it will be readily appreciated that these graduationsserve .to indicate the angular position' of the bracket 32 with respect to the base. The bracket 32 is provided with a longitudinally extending slot which provides means for adjustably mounting a tap holder support 35. As is best seen in Figure 5.. the tap holder support 35 is anchored in the desired predetermined adjusted position with respect to the bracket 32 by means of a large manually operated nut 36 threadably received on an externally threaded flanged bushing 31. The flange of this bushing 31 overlies and engages the upper surface of the bracket 32. A washer 38 surrounds the lower end of the bushing 31 adjacent the nut 36 and this washer is interposed between the nut 36 and the underside of the bracket 32; This structure is clearly illustrated in Figure 5. As is seen in Figure 5, the bushing 31 surrounds an internal bushing 39; fixedly anchored to the tap holder support 35 by means of a cap screw 40. Thetap holder support 35 has a downwardly extending flange 41 which meets with and slides against an upwardly extending flange 42' formed on the bracket 32, these flanges together serving to preelude any relative, rotative movement between the tap holder support 35 and the bracket 32.

7 From the foregoing, it is clear that the tap holder support maybe adjusted to any desired longitudinal position with respect to the bracket 32 rnerely by looseningthe hand nut 38 and. sliding the support to the position desired, thentightening the nut to lock the support in predetermined adjusted position. U

The tap holder support is provided at its upper end with a relatively large cylindrical bore there:- through. and it is noted that the axis of this bore is directly parallel to the slot in the bracket 32 and inasmuch as the. taptobe ground, when mounted in the manner hereinafter described, will be mounted with its .axis parallel to the axis of this bore, it is readily appreciated that the scale 34 described above mayserve to indicate the conical angle being ground on the point of the tap and it will likewise be seen that this conical angle may be varied as may be required by adjusting thepivotal position of the bracket 32 with respect to the base. I

This cylindrical bore through the tap holder support has anchored therein a concentric bearing sleeve 45 in which is rotatably mounted a flanged bushing extending axially throughout the length of the bore. As is clearly seen. this bushing 46 is provided at the forward axial end thereof with a flange 41 which overlies and bears against one axial end of the bore through the tap holder support. At the opposite end, this bushing is externally threaded and surrounded by a collar 48 anchored to the bushing to rotate therewith. The purpose and function of this collar are described in detail below. The bushing 46 is locked.

against axial movement with respect to" thetap holder support by means of a lock nut'49 threadably received on the bushing. This lock nut 49 forces the lock washer 48 against the tap holderv support sumciently snugly 'topreclude any axial movement of the bushing in the bore and yet at the same time permit rotation of the bushing in the bearing sleeve 45. a

The bushing 46 has mounted therein a that housing 50 which chuck housing is generally cylindrical in form and which, as will hereinafter be more clearly seen, -may' be concentrically mounted with respect to the bushing. The out side'diameter of the chuck housing is, however, I considerably smaller than the inside diameter of the bushing 46, thereby providing a clearance; designated as 5|, clearly shown in Figure l of the drawings. 'A chuck 52 of'conventional construction is rotatably mounted on a suitable bushing 53 interiorly and co-axially of the chuck housing 50. This chuck includes the conventional jaws 54 which may be closed to lock theshank of a tap therein in the conventional manner and it is inherent from the construction which'is described thatthe axis of the tap thus mounted will coincide with the axis of the chuck 52, bearing sleeve 53, chuckhousinglill, but will not'ne'c essarily coincide'with theaxis of the bushing '30 46, bearing sleeve 45, or the bore in the housing serve to, provide thev deslred-back-ofiangle, re: lief, or, chapter, for ,righthand taps and adjustment to .thexiesired degree of eccentricity in the 35, due to the mounting of the chuck housing in the bushing in the manner now to be described The chuck housing has the inner axial end thereof providedwith a flange of substantially the same construction asthe flange 41 on the axial ,end oi the bushing 46, and this flange as is shown in Figure 1, overlies the flange 41 on the bushing 46. The chuck housing 50 is anchored to the flange of'the bu'shing46 by meansof a pivot screw 56,]threadably received within the flange 41, and having a plain shank to permit pivotal movement of. the chuck housinglabout the screw to a limited extent. 0n the diametri cally opposite side of the flange of thechuck housing, the flangeis slotted :to provide an arcu ate slot, this slot being formedabout. an arc whose center coincides with the screw 56. Acaiscrew 51 passes through this slot andis threadablyreceived in the flange 41 of the bushing 46 in order that" the position of the chuck housing may be adjusted and anchored with respect to the bushing 46. 4

As is clearly seen in Figure 2 of the drawings. the periphery of the flange 41 is provided with a suitable series of graduations 58 which may be read from a line 59 on the periphery ofthe flange of the chuck housing. These'graduations serve to indicate the degree of eccentricity ofthe chuck" and chuck housing with respect to the bushing 46, and it will be reachly appreciated that as a result'of adjusting the pivotal position of the chuck housing 56 with respect to the screw 56, the amount of eccentricity between the chuck housing and the bushing 46 can be accurately adjusted to the desired amount and the chuck housing can then be anchored in'position with respect to the bushing in order to retain the same in predetermined adjusted position;

, As will be readily appreciated, the magnitude ofthis eccentricity determines the magnitude of the back-ofl' or relief produced back'ofthe cut- "holder-will cause rotation of the chuck housing ting edge of the tap land being ground and it I will be; seen that movement of the chuck housingto eccentric position in one'direction will the tap may opposite direction will serve to produce a similar result ,inthe event lefthand threaded. taps are to beground. .1 g I Referring "again to Figure, I of the drawings,*it will beseenthat the chuck 52 is formed ;to pro-% vide a'rearwardly extending cylindrical shank .65 whose axis coincides with the axis of the chuck 62. ,Keyed'to 'thisshank65-is a drum Such drum.may be a unitary. structure .ormaybe a plurality of discs securedv together and are axially slid'able' on the shank 65, but'are non-rotatably mounted with respect thereto. 1, The chuck hous-l ing 5|! includes -a radially extending boss 61 adjacent the'rear end thereof which servesto mount a bushing '68, providing. a cylindrical chore--11: which is mounted a plunger 69 whiclris con:- stantly urged radially inwardly by means of a compression coil spring 10. Adjacent one side of theboss'61 is a pivotally mounted-control'handle' 15 which serves two separate and distinct functions. handle ln'the first instance may bepivotally swungvabout :a pivot pin'16 and includesa projecting qlugill which is received in a complemental recess in the side of the plunger 69 whereby pivotal movement of the handle 15-about its pivot 16 will serve to withdraw the plunger 69,against the forceo'fthespring 16. e V: 7 The drum 66 at longitudinally spaced regions therealong or reach of the discs 66 hasa series of equally circumferentially spaced peripheral notches therein and. each of these regions ordiscs has a. 'difierent number of notches corresponding in number and spacing to the number and spacing of the flutes in the varioussizes of taps rear end of the chuckhousing. From the fore: going,jit is clear that when a tap is to be ground, be mounted in the chuck, the handle 15 may be swung about its pivot 16 to withdraw the plunger 69. The projectingend of the, index drum then may bewithdrawn until'the disc hav.-

ing' the samenumber and spacing of notchesas the number of spacing of the flutes in ,thetap is located opposite theplunger. The handle; 15 may then be swung so that the plunger en ages a peripheral notch in this disc. The rotative positionpof the tap in the chuckmaythen' bead;-

iusted so thatproper grinding will result from operation of the apparatus, as hereinafter'deascribed.

It will be apparent thatmovement of thehandle 15. arcuately about the axis of the chuck 50 and bushing-46 to which itisanchored, Inasmuch as the engagement of the plunger 69 with one'of 'the discs 66 serves to preclude rotational movement of the chuck with respect to the chuck housing, rotation of ;the chuck housing .and bushing 46 will cause similar, rotation of the chuck 52 and the tap mounted therein. However, as explained above, the chuck has its axis slightly offset from the axes of the bushing 46 and bearing 45. Consequently, the rotation of the .tapfwill not'be about the axis of the tapybut about the axis -oi? the ly eccentric withrespect thereto.

bushing 46 which is slight- As is mostclearly seen :in Figure 2, the collar '46 has a flangeiwhich overlies the exterior of the support 35 and. a portion ofthis flange is ,cut

away. The rotation creme assembly. Just descrihed within uietaip hinder supports: win cauw rotation of the collar 48 inasmueh' as eel-lair as unwed to the bushmg 1A 85 proiects :trern the tap holder :support dnd em gages the flange on the collar 48, as shown in Figure 2. A plurality holes '86 are pruvided in the enterior or the tap hbl'dei' support, "and a removable screw 8:! may be inserted in any or these holes as may "be desired. screw is preferably anchored to the. tap' hol'dr support-- ing housing by means of a chain 88'. The spac mg the :holes 86 with respect to the stop ipin is precisednd insertioncf the screw 81 in these holes, together with the stop pin and doliar 8-, serve to hrovide means :cr accurately and preciseiyeontroiling themagnitude of the rbtative movement of the chuck housing within the tap hzndersupnert.

It will be appreciated that the magnitude of the angular movement to which the tap is sub' jected during "the grinding cberation' will depend uponthenumber of flutes m the tap; Con sequently, the location of the remdvahle screw 8-1 may serve to adjust the apparatus Ior use'ih grinding taps having "any desired number of flutes. I

Tn e derte completely rte-condition taps it is necessary not only to grind the lands between the flutes, but also to grind the tapered portion of the flutes themselves, this letter operation-behis known semi pointing when carried out in the manner hereinafter described. in detail.

' Referring now specifically to that zporticn of the separates illustrated in the right hand p'ertion of Figure '2 or the drawings, "it win be seen that nae shaft Bl of the electric motor 12 has anchored thereto a; generally ifi'iis'to cbhic'al abrasive wheelm by means of a conventional nut 92. In inuch the same manner as at the op osite sneer the'hrotor, this abrasive wheel 81 is em erased witl'iih a suitable housing 83 permanently secured to the motor, the cpeh axial end or which naming is closed by means of a suitable cover 1318.475 93 by means bf S ci'eW'S '95. As is particiilarly clearly illustrated in F l'gu're 3 of the drawih gs, the housing 93 'a'fld c0378? plate 94 arecut away to expose a suitahle semen of the periph ery of the grinding wheel 92 in orderthat the grinding operations described below may be our- 'ried'out.

"The peripheral surface of the grinding wheel 91 is ressed by hahd in any convenient manner to provide aradius thereen of a curvature apbroximating the curvature or the flute it isdesired to produce in the spiral point of the tap to be ground. inasmuch as the form of this portion of the flute r the tan is'hot Particularly critical, handdressirig of the abrasiv wheel produces a sufii iently close form to produce the results desired in the grlndmgoperaticn. Y

' cans are provided for precisely, accurately; and positively adjusting the iJos'itiori or the tap to be ground for this spiral pointing ofler'atibn. This apbaratils is best disclosed in Figure 2 ofth'e drawings. In this figure, it is clear that the base It may be provided with a second end wall 84, spaced outwardly from the end wall 98 thereof and that these walls 84 and 86 may be rigidly interconnect d by means of a suitable Web 91.

walls 84- and at are provided with axially aligned bores which serve to receive a pin- 83, journalled for rotation therein. Wall 84 is provided around the bore with a boss 98 to which is secured a feed nut 89 by means of screws I00. 73

A reed-screw 11H hailihs an iihratfirg 1M attached thereto is threada'bry"recur ed in "the feed nut 99 and has its inner end anchored re the pin 83 through a ban bearing assembly 1'03. It is apparent from this construction that rota"- tion of the crank 102 wfi1 serve to accurately and precisely adjust the axial'positio ri of thezpin 88, but due to the int'rpositionbf the raceway 103, the pin 83 is free to rotate indefiendntly of the feed screw lfll.

At its opposite end, the pin 83 may be or reduced diameter and surrounded :by a torsion oil firing one endof whichis anchored to the pin and the opposite end of which is anchored to the base member. The purpose and function of this coil spring will become cleards the de scription of this portion of the apparatus pro= ce'ed's.

Permanently anchored to the pin substantial-1y centrally between the walls M and 96 is a housing I in which is locked, to the pinby mean-s of a set screw H I. This housing J threadably receives an adjusting screw 14 2 the-upper end of which is provided with a handle {43. The screw U2 is received in an internally threaded-bore H4 in the housing H0 and this housing also includes two smooth bores H5 and: H6 parallel to and on opposite sides of the internally threaded bore H4. These bores HS and '6 have anchored therein guide pins 1 1 and I 18, respectively, are slidably received within suitabl'bores through a member 119 which also has'a central here [28, through which passes an tinthreaded semen of the shank of the feed screw I I2.

nterposed between the handle H3 01 the feed screw and the upper end of the member 119 is a washer I22 and,similarly,a'washer l23 i pinned tol the screw H2 immediately below the member ins. From the above described eons'tmctien t will be seen that a the handle I Isis rotates, the vertical position of. the member H9 will be ddju'st'ed and at the same time the member H-Qfis positively retained against rotation relative to the housing In as e result of the guide pins in and 1 18, which permit vertical movement of the her 9, but positively 'Di'echid'e any rotational movement of the member H9.

The member 9 includes on one intern side thereof ab'oss or p'ad more which is secured a bracket [3| by means of a bolt I32 and-,- as is seen in Figure 1, this bracket and had the necrovided' with a scale I33 in order that the angular position of the bracket I 3| with respect to the ad I may be ecuratelyedjusted to the predetermined desired position.

Securedto the bracket 13! by means of a bolt 135 is a h'ofisfii I36 which serves to firv-ide means for rotatably inountin'g'a chuck l3! for holding a tap to be ground. This chuck 1-31 has a reafwardiy projecting shank I38 which extends through the housing I36 and has kefyed thereto a peripherally notched index disc [-39 in order to lock the chuck 131 againstorelative rotative movement with respect to the housing I313. The notches in the periphery of; the {index plate are :uiafmtcd'to cooperate witha lug-14G, pivotally mounted in the housing by means of a pivot pin ill, and it is seen that this lug I40 is urged to.- ward engagement with the index plate by means of a springpressed plunger 142;, ljhe extreme rear end of the shank lflto f the chuck i3! is provided with a knob l by which the chuck may be manually rotated when the lug 1 40 is wi thdrawntrom engagement with the index gilate I325. From the foregoing, it will be apparent that the a direction generally perpendicular to the cutting lug- I.40 may be, clisengaged from the index plate and the chuck holding .a tap to be ground may be rotated throughout the desired'angular distance between'the flutes, and the lug may then be engaged with the corresponding notch in the index plate to lock the chuck'against rotative movement while the grinding. operation takes place. The indexdisc I39 may beprovided with asufliciently large number of precisely spaced peripheral notches in order that this assembly.

will serve to accommodate taps.-;having;various numbers .of flutes within the range .desiredavi: I

Bearing inrnind the above described structure;

thespiral pointing ofa tap may. be. accomplished in the following manner. The grinding wheelv 92 first has the peripheral-surface thereof trued, to provide thereon aradius of. curvature approximating the radius of curvature to begroundon the spiral point of the tapunder'goingtreatment. The tap is then rigidly niounted'inthe chuck I 31, care being taken that the rotativepositionof the tap .with respect to the chuck is such that the flute Y to be ground will properlybe presented to the grinding wheel when the grinding operation com,-

mences. The bolt I32..may be loosened, and the bracket I3 I' is then swung. to a positionwherethe angle of engagement. of the tapwith the grinding wheel will closely approximate the conical angle of the tapered point of the tap.. L

. Inasmuch as the degreeof spiral, point ground on the tap. will be determined .by the. degreeto which the axis of the tap isofisetwith respect to the'pIane of rotation of the periphery of the grinding 4 wheel, adjustment of the handle I02 which operates the screw. IOI will'servetomove the tap axially of the grinding wheel to the pre-. determineddesired position. .The handle H3 may .then be reciprocated or swung in an arcuate path around the axis of; the pin 83, thus bringing the .tap point into generally. tangential engagement withthe periphery of the grinding wheel 92. .The magnitude of this movement toward the'grinding wheel zmay be precisely controlled by means of an adjustable-stopscrew I50 rotatably received in the housing web .91, the inner end .of the pin I50 engagingthe adjacent surface of the housing I I0, thereby limiting inward movement of the. tap tangentially of the grinding wheel. 'As the grinding operation takes place, the amount of grindingto be, done. may be increasedby rotation ofv the handle. I I3 whichwill cause an upward feeding movement of'the entire as-. semblywhich serves to mount and hold .thetap.

. When one flute of the tap has thus been ground, the lug I40 'may be withdrawn and the chuck holding; the tap. rotated throughout the desired.

the lefthand side of the assembly, as seenin Fig-:

ures 1 and. 2,. serves to grind the land or. chamfer back of the cutting edge, and the apparatus at the righthand side of theassembly serves to grind the flute. and side wall' ofzthe land 'adjacentzthe cutting edge 'Inasmuch as the grinding operation just described: serves to produce grinding wheel marks on the side wall of the flute which run generally longitudinally of the tap, and inasmuch as such grinding wheel marks tend to interfere to some extent with the removal of chips by the tap during a thread cutting operation, it is generally desirable in the re-conditioning of taps to give these spiral point flutes a slight finishing grind in order that any grinding wheel marks will run in edge in order to facilitate removal of chips by the .tap during the cutting operatiom In order'toaccomplish this last mentioned resuit, the apparatus includes, as is shown in Figure 5, an electric motor I60, housed within the base I0 of the apparatus. This motor. is controlledbymeans of a suitable switch IEI and has a shaft I62 extending through the front 'face of the base; To this shaft is anchored a *chuck I .63. which serves tomount a pencil grinding wheel I64 of relatively small radius. I The tap,- after having the flutes ground thereon by the apparatus as above describedimay'have each of the flutes subjected to the action of the pencil wheel I64 to an extent sufiicientto obliterate the longitudinal grinding wheel marks formed by the abrasive wheel92. Inasmuch as this last described operation is more Orless ofa finishing operationa'nd during it insuflicient stock is removed to materially vary the formof. the tapv point, no apparatus is needed for positioning the tap duringthis grindand merely hav'e'one flute after another brought into en'gagement with thepencil wheel I64..to an extent suflicient to obliterate any longitudinal grinding wheel mark left. by the wheel 92. .7

:In grinding the. chamfer or. relief back of the cutting edgeof. .the-tapon that portion of the apparatusshown at the le'fthand' side of Figures 1 and 2 of the drawings,' it will'be noted'that the tap holder support 35 isprovided at the upper side thereof with 'a projection I10 which serves to mount in adjusted longitudinal position a shaft I1I.; This shaft I" may be anchored in predetermined longitudinal position/with respect to the housing by means of a set screw I12, and theshaft may have pivoted thereto a locating arm I13 carrying alocating" finger. I14 adapted to'engage the flute between adjacent lands of a tap to be ground. This'assembly may conveniently be used if desired when mounting a tap in position in the .chuck 52 in order to insurethat theirelative "rotative position of the tap with respect to the chuck is adjusted precisely in the manner desired. After a tap has been thus adjusted in the chuck and anchored firmly in the chuck, the arm I13 may be-swung about its pivot so that it willbe out. of; the way during the grinding operation; The set screw 81 is then set in position 'i'n'one of the holes :86 in order that the angular movement of. the tap, caused by swinging movement ofthe handle 15 in a directionl generally arcuatelya'bout the axis of the tap, will be limited to the extent necessary, depending upon the number of flutes with which the tap is provided.'

The screw 51 is then loosened and the chuck holder adjustably positioned within the bushing with its axis offset from the axis of the bushing 46 to provide the desired magnitude of relief on the land of the tap being ground and, as is clearly apparent from the above described structure, this adjustment must be made inone direction for taps for cutting lefthanded threads, and in'the opposite direction for taps for cutting righthanded threads.- When this adjustment has been made, the screw 51 is set up to anchor the tap handle in fixed position with respect to the bushing 46 in order that the desired degree of eccentricity between the axes of these two members will be retained throughout the grinding operation.

The nut 33 is then loosened and the entire bracket '32 is swunghngularly to bring the tap into a position so that its axis makes the desired angle with respect to. the: axi's' of rotati'onlof the abrasive: wheel in order to provide thedegree of conical angle required ,on the point of the tab. The. screw 33 is. then tightened up in: order to anchor the bracket in predetermined; adjusted position The hand nut 3E1 maybe loosened and the: entire assemblg'z slid along the bracket to ad justythe tap point in position adjacent the periphery of the. grinding wheel. The? handle 15' is thenswurig ab'outits pivot. 16 in order to withdrawthe. plunger 6-9 from the index drmn 4 The index drum is then slid along the shank 652 01 the chuck until the: particular index disc having thesam'e number. of peripheral notches asthere are fiutesin the tap tdbeground lies oppositethe inner end of: the: plunger- 69. The handle 15 is then swung toeng'age the plunger with the'correspondingn notch.

. The motor I2; is. then started and, by. means or thebfeedscifew [8; the motor may be bodily moved toward: theta-p: to be; ground until the; periphery oithe, grinding wheel- 2 0icome'stinto engagexhent withithelandton which the. chanifen'is to be pro duged; As; this engagement takes. placeg-lqthe handle] 5 i'sswungrgenerally aboutztheaxis of'flthe tapiandi it: is noted that. the angular movement of this. handle. is limited. by'the stopi pin" 85'. and the set screw Us; whiclrtasiexplainedabove, has been; insertedin; an; apertufe so that the angular moyein'ent will be; controlled in accordance with may be maderwithbut: departing frointhe generic;

spirit, and? scope ofithe invention as. set rortnm thezls'ubjoinedjclaim's. c

.Whatis:clainied-isz;v s c 14in" alitdpjemonditioningvmachin' for grind:- ing: Ithechamfenon; as nap-1 tojibe. ground comprise ingiai chuck-housing: rotatable; about an. axis ofi setz iromrits; own axiszra ch'uck rotatable. in said: chuck-housing: the. axis or; said chuck; coincidingi withzthe'; axis: of said; chuck hoi'ising, w an index dnumljearrled by.said ch1ic1;.said'.drm' including. a pluralityabf;peripheralnotchesanguiarly"spaced;

in accordancexwith the] spacing: or the'a'flutes "on the tap :to ,1 lie-ground; and: means carried-by said chuck; housing; adapted to; engage, one ofthey notches in saidindex drum to; lock said, :chuckagainst rotative movement in: said chuck nousing.

2.: A: holder; asser nbly usefnlin grinding;

the chamijer on the; point-of atap, ,inc1uding, in

combination, a .housing hayinga cylindrical bore 1 therein; a bushing rotatablygdisriosedawithinzisaide bore and having the axisfiot its bore coincident.

with theaxis of said first na med:bore,,a:tubumo em 1a: chuck housing disposed within said Bushing and spaced from the mnersuiracetrrerof; a tab holding 'cliuck adaptd t meumexiaiiy thereorv a tap to'ib greuim mountee witfim smd amid; housing with its axis 'eoineidem with the axis of said. chuck housing, and adjustable mes inter connecting said chuck housing find said bfis'hihg for oiis'ttinggthe axis of said clia cizwith respect to. the axis of isa-id biisl i-ir'ig withinsliid space therebetween I i A tap :liolder asseihiiiy' ii'semi-img ri num the the axis or its bore coiheiaem; A sei'd first named Bore; a tubiiliii chuck housi'n disposed Within said bushing. and spaced from-the inner surface thereof, a tap holding 'chiick adapted to mount axially there- (are tap-to bezgroimu mdunteu Within said ehuk h'ousi'ng- Witt-tits axis eoihiuentwithi the axis or: said: biruok: housing means piviitaily conneet: ing said ehuekhousing: "and gem b'usming for swinging: movement-about saidv pivot: within" said spae'e-therebetwenz tboflset the axis: otsam chuck with: respect to: the: axis: of: sem bushing; and means to: libltt saim chock: housing in: its onset positioir. a

4 A tap holder ass-ammo the. en'amferon'tne point of sti t nclddifig' in 1dr chuck; housing disposed: within: seid bushin'g and; spacedirdm the-dimer ear-race thereof, a tan holding fchuck adaptecttb mount axiali=ithere'-' crate- [to .be groundarotetably mmm'ted Within saith chu'cin Housing; with its axis icc'iincfdent with the axis bfzfsaid chuck? housing; 'and' adjustabi'e means interconnecting said 'e'imck housing and s'aidzbushingtfmr:ofisetting: the ai'zis ofisai'd 'chuck Witha respect to athef axis or saidi bushing with-in said sp'e therebetweeria V 7.5: m. tapliofder. assembiy useful in: grinding: the: chmfeif on: the point; of. tafa; including, in; cmnliimrtiong, 'afhou'sing: having: a, .cylindi'ical bore: therein; a bushiiigihaving 'a' radia'l flange onl one. end. "thereof Irotatabi disposed withfn' 0I17fidi thereof .disposed within 'saidibushingt'lirid spaced from we imier" "smitail'ce tlfere'of, 'a; tap

: holding :rchuiskmdapted tdmount alxiili'y thereoffi wra 'toctie grou'nd- -nfoui td within said --chiick hou'singi with; its: axis coincident with. the axis of said chuokgghonsirrg zsand .me'alnls bivo'tal'ly? 'conn'ectin'g*rthe cflafigesz of sai'd i'chucki 'hot'ising 'a'nd sai'di bushing: for nmvemenr, "lfi saidchuckaliousirigi .witlfinisaiidsiiacetherb'etweenrto offset the; of? said: chuck with respect? tofthe axis-10L "said; "h.u sliingr; .;and means-i diametricailyz opposedrto' saidmivot meains: to i hold said chuck housing in its offset position. 

